Beginner Exercise 170 / Solution

Black lives (mostly)  

I may be wrong, but I think living with this top group is the best black can do... I see no way for the bottom group to live. I'd be interested in seeing if there's any better outcome :) --Hikaru79

JoelR: White can choose to fight a ko for the whole group instead, by playing at . And even if Black starts with , White can play to the same ko.

LukeNine45: Exactly what I had in mind.

White lets the top live  

ChrisSchack: (In response to the original diagram): White wouldn't play this way if not planning to start the ko, it gives up 4 points for the same result.

LukeNine45: You're right, this is a much more consistent way for white to play. (If you delete our exchange after you read it, the page will make a little more sense for the passer-by :)

White wants to fight a ko.  

This ko does not favor white, as black takes first and white will need a huge ko threat.

Not so good for White  

If, instead, White plays , - is Black's ko threat.

This shows that is not a good first play for Black. First, it loses the chance for this ko threat. Second, if White loses the ko, it gives up a sure 1/2 point to White at a, which White does not get if her first play is . This makes the ko worth slightly less and slightly more favorable for White. And, of course, if White avoids the ko, makes more territory. Either way, is better for Black than .

All of these are very minor points, but fairly clear. Avoiding should be a no-brainer.